Low Normal Force Retracting Device Comprising a Microtextured Surface

ABSTRACT

Retraction of one or more three-dimensional or planar amorphous objects is provided to gain access for a procedure where the retracted elements are easily damaged by application of normal forces. For example, a surgical instrument to provide access to an organ or tissue plane. Microtextured surfaces are provided that provide immobilization of amorphous objects, the immobilization of which is characterized by low normal forces and high shear or in plane forces. The retraction device is comprised of microstructured surfaces on one or more arms. Preferably these arms are soft and flexible to minimize damage to retracted objects. In some instances, these arms resemble and are used as a nonslip tape. Alternatively, parts or whole arms of the retraction device are rigid to provide a supportive aspect. These arms may be configured around a handle. Furthermore, the microtextured aspect may be further augmented with conventional gripping surfaces, such as a sticky surface, or a surface comprised of one or more hooks or barbs. The handle means may be distributed over the retraction device, for example, holes distributed along the arms through which anchoring means are tied. The retraction device is particularly well suited for grasping wet, oily, slimy or living surfaces by applying a small nondestructive normal force.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.62/237,448 filed on Oct. 5, 2015, the contents of which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to surgical retractors comprisingmicrotextured surfaces. The surgical retractors comprise a microtexturedsurface on one or more portions of the retractor, thereby advantageouslyproviding immobilizing or positioning forces to a wet tissue surfacewhile preventing or minimizing damage or trauma to the tissue.

BACKGROUND

There are many objects, natural and manmade, that are characterized bypossessing a relatively durable surface enclosing delicate structuresthat would be adversely altered by a force applied normal to the durablesurface and unaltered by a force applied tangent or in plane to thedurable surface. Therefore, there is a need in the art for a retractingdevice that allows these objects to be immobilized, relocated, orpositioned without causing internal damage by the force applied by theretractor.

A non-limiting example is the traction of living tissue during a medicalprocedure such as a surgery. In these procedures it is frequentlynecessary to retract organs to gain access to a target organ or tissueto be treated or observed. In other procedures, to gain access to theorgan or tissue to be treated or observed, it is necessary to separatethe organ to be treated from tissue surrounding it. For example, to beable to observe the outer surface of the heart, it must be separatedfrom the pericardium. To obtain the necessary retraction, currentlaparoscopic procedures use several small retractors inserted through aplurality of incisions. Because such retractors have a relatively smallsurface area, they tend to damage and/or cause trauma to the retractedorgans or tissue by applying localized normal forces.

Wenzel, Cassie and Wenzel-Cassie states describes wetting phenomenabetween hydrophobic and hydrophilic components of a mixture at a surfaceinterface. The interaction of a solid textured surface with water in agaseous environment is described by the Cassie-Baxter model. In thismodel, air is trapped in the microgrooves of a textured surface andwater droplets rest on a compound surface comprising air and the tops ofmicroprotrusions. The importance of a fractal dimension between multiplescales of texture is well recognized and many approaches have been basedon the fractal contribution, i.e., the dimensional relationship betweendifferent scales of texture.

However, regardless of the material (organic or inorganic) used andgeometric structure of a surface texture (particles, rod arrays, orpores), multiple scales of texture in combination with low surfaceenergy would be needed to obtain the so called superhydrophobicsurfaces. Superhydrophobicity is variously reported as a materialexhibiting a contact angle with water that is greater than contactangles achievable with smooth but strongly hydrophobic materials. Thegeneral consensus for the minimum contact angle for a superhydrophobicsubstance is 150 degrees.

A hydrophobic surface repels water. The hydrophobicity of a surface canbe measured, for example, by determining the contact angle of a drop ofwater on a surface. The contact angle can be measured in a static stateor in a dynamic state. A dynamic contact angle measurement can includedetermining an advancing contact angle or a receding contact angle withrespect to an adherent species such as a water drop. A hydrophobicsurface having a small difference between advancing and receding contactangles (i.e., low contact angle hysteresis) results in surfaces with lowresistance to in plane translation (low adherence). Water can travelacross a surface having low contact angle hysteresis more readily thanacross a surface having a high contact angle hysteresis, thus themagnitude of the contact angle hysteresis can be equated with the amountof energy needed to move a substance.

The classic motivation from nature for surface texture research is thelotus leaf, which is superhydrophobic due to a hierarchical structure ofconvex cell papillae and randomly oriented hydrophobic wax tubules,which have high contact angles and low contact angle hysteresis withwater and show strong self-cleaning properties. A lesser knownmotivation from nature is the red rose petal, with a hierarchicalstructure of convex cell papillae ornamented with circumferentiallyarranged and axially directed ridges, which have a moderate contactangle and high angular contact difference.

The contact angle is a measure of the amount of water directly incontact with the textured surface, while the contact angle hysteresis isa measure of the degree to which water is mobile on a surface. Theevolutionary motivation for each of these states is quite distinct. Inthe case of the lotus leaf, and botanical leaves generally, minimalcontact with water and high water mobility results in preferentialadherence of the water to particulate contaminants, which are clearedfrom the leave as the water runs off. This serves to reduce to theamount of light absorbance by surface contaminants, and increasephotosynthetic efficiency. In the case of the rose petal, and botanicalpetals generally, most pollinators are attracted to high tension watersources which provide ready accessibility without drowning the insect.Thus, high contact angle paired with high contact angle hysteresis ispreferred where the evolutionary stimulus is reproduction in botanicals,and high contact angle paired with low contact angle hysteresis ispreferred where the evolutionary stimulus is metabolism and growth.

Considering for a moment a single texture scale, when water is placed ona textured surface it can either sit on the peaks of the texture or wickinto the valleys. The former is called the Cassie state, and the laterthe Wenzel state. When the Wenzel state is dominant, both the contactangle and contact angle hysteresis increase as the surface roughnessincreases. When a roughness factor exceeds a critical level, however,the contact angle continues to increase while the hysteresis startsdecreasing. At this point, the dominant wetting behavior changes, due toan increase in the amount of hydrophobic component (in this case, air)at the interface between the surface and water droplet. When multipletexture scales are employed, some can be Wenzel and others Cassie. Ofthe two states, the Wenzel state has the lower contact angle, highercontact angle hysteresis and lower mobility. In mixed Wenzel-Cassiestates it is possible to have high contact angle and high contact anglehysteresis. However, the hydrophobicity of a textured solid relative tothe interacting hydrophobic and hydrophilic components is veryimportant.

In the botanical world, most textured surfaces occur on substrates thatare hydrophobic. However, when a hydrophobic fluid replaces the water, aCassie state can easily be converted to a Wenzel state. This is notalways the case, and depends on the vapor pressure and viscosity of thehydrophobic material and how quickly the air trapped in the surfacetexture can be dissipated.

Various attempts have been made to achieve hydrophobic coatings andsurfaces, as follows: U.S. Pat. No. 6,994,045 describes asuperhydrophobic coating acting as a substrate for a gaseous lubricantof very low viscosity, has a hierarchical fractal structural of thesurface wherein the forms of the first hierarchical level are located atthe coating's substrate, and the forms of each successive hierarchicallevels are located on the surface of the previous hierarchic level andthe forms of individual higher hierarchic levels reiterate the forms ofthe lower hierarchic levels. U.S. Pat. No. 7,419,615 discloses a methodof forming a superhydrophobic material by mixing a hydrophobic materialwith soluble particles to form a mixture. U.S. Pat. No. 7,887,736discloses a superhydrophobic surface repeatedly imprinted using atemplate, so that mass production of a superhydrophobic polymer over alarge area can be economically implemented. U.S. Pub. No. 20030147932discloses a self-cleaning or lotus effect surface that has antifoulingproperties. U.S. Pub. No. 20060029808 discloses a coating that canremain superhydrophobic after being immersed in water for one week. U.S.Pub. No. 20080015298 discloses a superhydrophobic coating composition.U.S. Pub. No. 20080241512 discloses a method of depositing layers ofmaterials to provide superhydrophilic surface properties, orsuperhydrophobic surface properties, or combinations of such propertiesat various locations on a given surface. U.S. Pub. No. 20090011222discloses a method of applying lotus effect materials as asuperhydrophobic protective coating for various system applications, aswell as the method of fabricating/preparing lotus effect coatings. U.S.Pub. No. 20090076430 discloses a bandage that includes a material, whichcan be breathable, having a first surface, and a plurality ofsuperhydrophobic particles attached to the first surface. The materialcan have a second surface opposite the first surface that ishydrophilic. U.S. Pub. No. 20090227164 discloses a superhydrophobiccoating of a nonwoven material is coated with a spongy mesh structure inthe micro and nano ranges. U.S. Pub. No. 20100112286 discloses controland switching of liquid droplet states on artificially structuredsuperhydrophobic surfaces. U.S. Pub. No. 20100021692 discloses a methodof manufacturing a multiscale (hierarchical) superhydrophobic surface isprovided. The method includes texturing a polymer surface at three sizescales, in a fractal-like or pseudo fractal-like manner, the lowestscale being nanoscale and the highest microscale. U.S. Pub. No.20100028604 discloses a superhydrophobic structure comprise a substrateand a hierarchical surface structure disposed on at least one surface ofthe substrate, wherein the hierarchical surface structure comprises amicrostructure comprising a plurality of microasperities disposed in aspaced geometric pattern on at least one surface of the substrate. U.S.Pub. No. 20110077172 discloses a method of localized deposition of amaterial and includes a superhydrophobic substrate comprising raisedsurface structures

Accordingly, it is an object of the present invention to provide lownormal force retractors that create and adherent Cassie and Wenzelstates when placed in contact with wet living tissue.

BRIEF SUMMARY

The present disclosure relates to a low normal force retraction devicethat mechanically retracts surfaces or objects by applying a low-slipmicrotextured surface. In its simplest embodiments, the retractiondevice is comprised of one or more arms, jaws or tentacles forretracting an object. These features will be referred to collectively as“arms”. The arms in some instances are soft and flexible in a normaldirection, and substantially non-distensible in a tangent direction. Inother embodiments, one or more arms may be rigid so as to provide alifting or supportive function, such rigid arms will typically havelarger surface area to minimize the normal force per unit surface areaduring a lifting or retention application.

In other embodiments, the retraction device may consist of a singleflexible arm with a microtextured surface that is particularly usefulfor encircling an object to be retracted. Retraction in this case mayinclude folding one portion of an object over another portion of thesame object and holding the folded object in this configuration. Whenthe retraction device is a single flexible arm, it maybe furtherequipped with other fastening features such as holes or hooks that canbe used to anchor the arm to an external anchoring structure. Theseadditional fastening features may be employed in coupling two or moresingle arm retractors together. These additional fastening features mayinclude without limitation lockable graspers, such as a pliers orforceps.

In the following description, the term “microtextured surface” will beused to mean a surface with a hierarchical structure comprised ofmicrostructures of various spatial scales superimposed to form a singlesurface with texture on at least two spatial scales. In someembodiments, the microtextured surface comprises three, four or morespatial scales, preferably three or four spatial scales. Examples ofmicrotextured surfaces useful in the present retractors includesuperhydrophobic surfaces resembling natural rose petal texture. Otherexamples include surfaces whose contact hysteresis with living tissue isgreater than 5 degrees. These surfaces are characterized by theproduction of a Wenzel-Cassie interface when the microtextured surfacecomes into contact with a wet or lubricious surface. Other, hierarchicalmicrotextured surfaces include those resembling the surface texture of alotus leaf, wherein the interface is a Cassie-Baxter type interface.

A microtextured surface may comprise a hybrid of the above-mentionedrose and lotus surface textures wherein one portion is rose-like andother portions are lotus-like, to obtain a “rotus” surface. An arm ofthe present invention may have a lotus surface on one side and a rosesurface on the other side. In the following description, the word“normal force” will be used to mean a force per unit surface area orpressure, wherein the force is orthogonal or normal to the surface area.The surface area typically will refer to the textured surface area ofthe microtexture arm, and the normal force that force orthogonal to thetextured surface of the arm that is applied through contact with anobject to be retracted. Accordingly, the normal force can generally bedecreased by increasing the surface area of the arm. In some instancesit may be useful to be able to alter the surface area of themicrotextured arm. Accordingly, the arm may have a corrugated structurethat can be made less corrugated to increase the arm's surface area.Other retractors include inflation or distention of the arm. In stillother embodiments, the areas of increasing area are decoupled frommicrostructured areas where the microstructure spatial dimensions areunaltered by the act of increasing the surface area of the arm. Theinflation aspect may be used to alter the rigidity of the microtexturedarm, or alter its morphology. For example, inflation of twomicrostructured arms may be configured to create a pincer movement thatprovides for the alteration of the applied normal forces.

According to different aspects of the invention, microtexturedretraction devices according to the invention employ different ways toretain their ability to provide retraction while providing access forother instrumentation to the object to be treated or observed. Amicrotextured retraction device according to one aspect of theinvention, such a retraction device being designated generally as a TypeI retraction device, provides retraction by a Wenzel-Cassie effect alonewherein the microtextured surface naturally adheres itself by ahydrophobic interaction with wet surfaces. Type I devices typically havefixed mechanical properties, such as elasticity, rigidity, modulus, andthe like. Type II devices include auxiliary components for alteringthese characteristics and the relation between arms. For example,stiffening an arm or bring two arms to a preferred orientation byinflation. Inflation includes both gaseous and liquid inflation. Ingaseous inflation, pressure is controlled, while in liquid inflation,volume is controlled. Composite inflation structures are possible. Afirst inflation chamber can be formed between two opposing surfaces of atube-shape microtextured arm, wherein bridging structures betweenopposing surfaces maintains an approximately flat tape-shapedmicrotextured arm under inflation. An additional inflatable chamber,which forms an inner smaller tubular structure inside the first chamberof the microtextured arm. Under inflation, this second chamber mayprovide a preferred curved structure to the microtextured arm. Thesecond inflatable chamber is normally inflated after the main inflatablechamber of the retraction device has been inflated, and the retractiondevice has produced its desired retraction effect. Such an additionalinflatable chamber is smaller and less powerful than the main inflatablechamber. Inflating the additional chamber alone would not always producesufficient force to provide the desired retraction of the organ.However, the inflated additional chamber provides enough force tomaintain an object that has been retracted by the more powerful maininflatable chamber in its retracted position. The additional inflatablechamber is thus able to maintain the retraction effect of the retractiondevice after the retraction effect of the main inflatable chamber hasbeen destroyed by piercing an aperture in the envelope of the mainchamber to provide access to the object to be treated.

A Type I or a Type II retraction device according to the invention maybe provided, according to a further aspect of the invention, with tabsattached to the surfaces of the microtextured arms of the device. Thetabs are gripped with a suitable gripping tool to adjust the positionand orientation of the retraction device relative to the tissue to betreated.

According to a further aspect of the invention, a Type I or a Type IIretraction device may be provided, when in its first state prior toactuation, with markings on its surface to aid proper orientation priorto actuation or similar markings intended to indicate regions ofdifferent surface texture. According to a further aspect of theinvention, a Type I or a Type II retraction device can possess acorrugated surface wherein one configuration of the corrugation providesan adhesive Wenzel-Cassie surface and in another configuration of thecorrugation provides a low friction Cassie-Baxter surface. This featuremay be used to release a retracted object in a manner that would reducepotential damage to the object if release was attempted while in theWenzel-Cassie state. For example, a Type I device could be in a firstadhesive state and subsequently made nonadhesive by irreversiblydeforming the microstructure arm by applying a tangent stretching motionto the microtextured arm. In a Type II device, the same can be achievedreversibly by an inflation action.

According to a further aspect of the invention, in a retraction deviceaccording to the invention, an arm may be incorporated with a suctiontube for removing free liquid at the retraction site. Alternatively, amicrostructured arm may be fitted with an attachment for such a suctiontube. In the case of retraction during a surgical procedure, suctionaspect is connected to the operating room suction line and allowscontinuous or intermittent drainage of fluid that collects in the bottomof a surgical cavity created by the retraction device duringlaparoscopic surgery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a superhydrophobic Wenzel-Cassiesurface embodiment of the invention;

FIG. 2 is a perspective view of a tape-like Type II inflatableretraction device according to a second embodiment of the invention;

FIG. 3 is a perspective view of a Type I retraction device fitted with asuction means according to a third embodiment of the invention.

FIG. 4 depicts a microstructured surface useful for a low normal forceretractor.

FIG. 5 depicts a first embodiment of a low normal force retractorsurface.

FIG. 6 depicts a second embodiment of having an inverse surface.

FIGS. 7A-7D depict a selection of substrates 710 having varioussinusoidal waveform patterns that provide alternative curved surfacetexture features across substrate 710

FIG. 8 depicts a side view of an embodiment of the microstructuredsurface on a substrate according to the present disclosure having asecond set of features disposed on the surface of the substrate.

FIG. 9 depicts a side view of another embodiment of the microstructuredsurface on a thin substrate according to the present disclosure.

FIG. 10 depicts a perspective view of a microstructured surface having afourth set of microfeatures.

FIG. 11 depicts a schematic top view of a microstructured surface havinga fourth set sets of microfeatures.

FIG. 12 is a perspective view of a hybrid rotus Type I retraction deviceaccording to another embodiment of the invention.

FIG. 13 is a perspective view of a corrugated Type II retraction deviceaccording to another embodiment of the invention.

FIG. 14 is a perspective view of a area changing Type II retractiondevice according to another embodiment of the invention. Device 1400 hassurface texture 1414 and can be in two configurations 1410 and 1412.Configuration 1410 is a flat configuration with maximum surface area incontact with a planar surface and configuration 1612 is an inflatedconfiguration with minimum surface area. Thus, when in configuration1710 device 1700 is adhesive, and in configuration 1412 it slides moreeasily. An inflation member 1416 causes device 1400 to transform intoconfiguration 1412 when pressurized.

FIG. 15 is a side view of a hybrid area changing Type I retractiondevice 1500 where the textured area 1514 is unchanging according to asixth embodiment of the invention. Device 1500 assumes two bistableconfigurations 1510 and 1512. In configuration 1510 rose petal texture1514 is the only surface presented to another surface to which device1500 is to adhere. The contact surface area in configuration 1510 is thesum of the areas of 1514. The area 1516 is smooth, and the area ofconfiguration 1512 is larger than the area of configuration 1510. Thearea of configuration 1512 is the sum of the areas 1514 and 1516.Configuration 1512 is achieved by pulling configuration 1510 in thedirections 1518.

FIG. 16 is a perspective view of a pincer movement Type II retractiondevice 1600 according to a seventh embodiment of the invention. Device1600 has a relaxed, conformable state 1610 and rigid pinching state1612. Transformation from state 1610 to state 1612 is achieved byinflation means 1616. Features 1614 are comprise a rose petal adhesivesurface.

FIG. 17 depicts a retractor comprising an arm having the microtexturedsurface of the present disclosure disposed on a portion thereof.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates. At least one embodiment of the present inventionwill be described and shown, and this application may show and/ordescribe other embodiments of the present invention. It is understoodthat any reference to “the invention” is a reference to an embodiment ofa family of inventions, with no single embodiment including anapparatus, process, or composition that must be included in allembodiments, unless otherwise stated.

Type I Devices

FIG. 1 shows a vertical view of a first embodiment 100 of a retractiondevice according to the invention. This type of retraction device isessentially fixed in its mechanical and geometrical aspects and will bedesignated as a Type I retraction device. The retraction device is shownin its flat condition, and it is understood that the device hassufficient flexibility that it can be made to conform to the surface ofan object to be retracted. The retraction device 100 comprises a firstside 102 and a second side 104. Retraction device 100 is made of arelatively inelastic and tough film of a plastic such as polypropylene,polyethylene, or polyurethane. The preferred material is a polyethyleneand nylon composite. The thickness of the retraction device 100 istypically from 0.5 to 5 mm. A surface texture 106 is comprised of largescale structure 108, intermediate scale structure 110, and microscalestructure 112. The microscale structure 112 is superimposed onintermediate scale structure 110, and this combination is superimposedon large scale structure 108. Large scale structure 108 has acharacteristic dimension between 100 and 1000 microns. Intermediatescale structure 110 has a characteristic dimension between 25 and 100microns. Microscale structure 112 has characteristic dimension between 1and 25 microns.

Generally, the size and shape of the retraction devices are applicationdependent. For example, in a surgical application, the size ofretraction devices according to the invention can range from about 2″(50 mm) long by about 0.5″ (12 mm) wide, for use inside the pericardium,to 10″14″(250-350 mm) long by 2″8″ (50-200 mm) wide, for use in theabdominal cavity. The size of retraction device required for a givenapplication depends on the application and the size of the patient.

Type II Retraction Devices

The basic embodiment of a Type II retraction device includes a singleinflation chamber. In alternative embodiments, a single chamber can bedivided into a plurality of subchambers. The subchambers are isolatedfrom one another, so that if one or more of them is accidentallypunctured while the retraction device is in use, deflation of all of theretraction device can be avoided. Each subchamber can be equipped withits own additional inflation tube. Alternatively, each subchamber can beconnected to an inflation manifold through a nonreturn valve. Themanifold arrangement requires that each subchamber be individuallydeflated in preparation for withdrawing the retraction device from thebody at the end of the treatment procedure. The main advantage of thesesubchambers, intercommunicating or separate, is to define a preferredgeometry under inflation.

FIG. 2 is a perspective view of a Type II device 200 with multipleinflation chambers. The main envelope 202 is made of a relativelyinelastic and tough film of a plastic such as polypropylene,polyethylene, or polyurethane. A preferred material for the mainenvelope is a polyethylene and nylon composite. The wall thickness 204of the main envelope 202 is typically from 0.5 to 5 mils (13 to 130microns). When inflated, the device thickness 206 of the microstructuredarm 200 is between 1 mm and 5 mm. The device thickness 206 is limited byheight 210 of inelastic members 208 that form the individual subchambers212. Subchambers 212 run to a manifold 214. Air or liquid pressure isdelivered by tube 216. The delivery tube 216 can be small and flexiblewith diameter 218 in the range 1 mm to 5 mm. The main inflation tube 216allows an inflation gas to pass into and out of the subchambers 212. Aninflation gas is typically air, nitrogen or carbon dioxide, althoughother suitable gases may be used. An inflation liquid is typicallyphysiologic saline. Typical inflation gas pressures are in the range 0.3to 0.7 psi (0.21 to 0.48 Pa), the preferred pressure being 0.5 psi (0.35kPa). Once the device 200 is fully inflated, the inflation gas pressurecan be reduced to about 0.3 psi (0.21 kPa).

Additional Features to Type I and Type II Devices Suction Aspect

According to a further aspect of the invention, a retraction deviceaccording to the invention may be fitted with a tubular suction portionon the part of the retraction device that is lowermost when theretraction device is deployed in a cavity with liquid present. FIG. 3shows a Type I device with the suction feature attached. The suctionportion of this aspect of the invention can be used with Type I and TypeII retraction devices. Irrigation is often used when retraction isapplied to a cavity environment. The irrigation is used to clear awaydebris. In the case of a surgical applications, the debris consists ofblood and clotted elements. This fluid collects in the bottom of thecavity in the body created by the retraction device and needs to becleared away. The suction portion 302 is integral to microstructuredretractor 300. The bottom of the retraction device 300 is connected to asuction line 302 and removes such fluid during the treatment procedure,keeping the cavity clear of accumulated fluids. In the example shown,the suction portion 302 is a tubular appendage attached to the lowermostextremity of the retraction device. The suction portion can be made ofthe polyethylenenylon composite that is the preferred material for themain body of the retraction device. This material is sufficientlyresilient that a tubular structure made from it can retain its opencross section under a low vacuum. One end of the suction portion 302 isclosed; the other is connected to a thin wall polyethylene tube 304 thatruns up the side of the retraction device to exit the body through thesame incision through which the retraction device is delivered. Suctionis delivered to the operative site through holes 306.

Curved Retraction Devices

Curvature can be formed within a tape like microstructured retractorarm. For example, the curvature may have a radius of curvature that issubstantially less than the length of the retractor such that when inthe relaxed state the arm curls on itself at least 1 time. The preformedradius of curvature along with the stiffness of the materials useddetermine the normal force when the object enclosed in the retractor islarger than the radius of curvature. In most cases, the normal force isproportional to the ratio of the object's diameter to the retractorsradius of curvature.

Referring to FIG. 4, generally a surface for an low normal forceretractor surface 400 of the present invention possesses a hierarchicalsurface comprised of a large scale structure 402 with a plurality ofprotuberances 404 and depressions 406 disposed in a geometric pattern onat least one surface of a substrate 408, and a medium scale structure410 disposed on at least one surface of the large scale level structure402 is comprised of protuberances 412. The small scale structure 414 issimilarly comprised of protuberances 416 and depressions 418 disposed onthe medium scale structure 410. The large scale protuberances 404 shouldbe high enough so that a hydrophilic component of ahydrophobic/hydrophilic contact mixture does not touch the large scaledepressions between adjacent protuberances 404. In the embodiment ofFIG. 4, the large scale protuberances 404 may comprise a height H ofbetween about 25 to about 1000 microns and a diameter D of between about25 to about 2000 microns, wherein the fraction of the surface area ofthe substrate 408 covered by the protuberances 404 may range frombetween about 0.1 to about 1.0. The medium scale protuberances 412 maycomprise a height 420 of between 5 to about 25 microns and a diameter422 of between 5 to about 50 microns, wherein the fraction of thesurface area of the substrate 408 covered by the protuberances 412 mayrange from between about 0.1 to about 0.9. The small scale structure 414may be disposed primarily on the medium scale structure 412. Thearrangement of hierarchical structures may be geometric and describablegenerally with a mathematical equation. Alternatively, the hierarchicalstructures may be randomly disposed, possibly with varying pitch, whichis more typical of natural structures. The arrangement of hierarchicalstructure can generally be described by a fractal dimension.

A fractal dimension is a statistical quantity that gives an indicationof how completely a collection of structures appears to fill space, inthe present case a plane, as one examines that structure on amultiplicity of spatial scales. Specifying a fractal dimension, which isstatistical in nature, does not necessarily indicate that thehierarchical structure is well defined by a mathematical equation.Generally, a random arrangement of structures within a specific scalepossesses a higher fractal dimension than one in which the structure ismathematically described at all points on a surface. Thus, a randomstructure may possess an advantage in the aspect that an adhesivesurface of the present invention has greater utility when interactingwith a natural surface. A higher fractal dimension within a specificspatial scale may be achieved by applying to a substrate multiple pitcharrangements. The protuberances and depressions may be locally scaledwith respect to the local pitch. Accordingly, the pitch may vary withina scale structure. In the practical realization of higher fractaldimension structures, the variation of the pitch may be describable by amathematical equation, for example, a sinusoidal variation of pitch,which would have utility in mimicking natural surfaces.

Generally, structures can be described as sharp-edged or rounded, andthis feature is not typically captured by a fractal dimension. Anotherstructural aspect not addressed by the above descriptive parameters isthe degree of communication between structures. By communication, it ismeant that a structure, such as a protuberance or a depression, has aspatial extent greater than the pitch. For example, a valley surroundinga protuberance may be connected to another valley surrounding anotherprotuberance, thus the depressions are said to be communicating whereasthe protuberances are not. The communication may range from 1 to about1000, more particularly the communication may extend over the entiresurface of the substrate. These structures are constructed with thepurpose of creating Wenzel and Cassie states, on a multiplicity ofscales, when the low normal force retractor of the present inventioncomes in contact with a hydrophobic/hydrophilic contact mixture.

A scale of interaction is defined by the surface texture of the presentlow normal force retractor, and is typically hierarchical, andcharacterized by at least two spatial scales, one on the order ofmicrometers (microns) and another on the order of 100s of microns. Thesurface texture may induce one state with a large difference betweenpreceding and receding contact angles (contact angle hysteresis), oralternatively another state with a small contact angle hysteresis.States of interest are known respectively as Wenzel and Cassie states.Each of the hierarchical spatial scales may induce separately a Wenzelor Cassie state, such that combinations are possible on a multiplicityof spatial scales.

These states are phenomena between hydrophobic and hydrophiliccomponents of a mixture residing at a textured surface interface. In theCassie state the adherent textile is resistant to hydrophobic debrisadhesion, for example oil in an oil water mixture. In the Wenzel statethe implant is reversibly adherent to a hydrophilic surface, for examplea wet or ice surface. In hybrid Cassie-Wenzel states, where one texturescale is Wenzel and the other is Cassie, the retractor can be bothlocalizing to a wet surface and resistant to hydrophobic contaminantssuch as fats.

The interaction of a solid textured surface with water in a gaseousenvironment is described by the Cassie-Baxter model. In this model, airis trapped in the microgrooves of a textured surface and water dropletsrest on a compound surface comprising air and the tops ofmicroprotrusions. The importance of a fractal dimension between multiplescales of texture is well recognized and many approaches have been basedon the fractal contribution, i.e., the dimensional relationship betweendifferent scales of texture.

However, regardless of the material (organic or inorganic) used andgeometric structure of the surface texture (particles, rod arrays, orpores), multiple scales of texture in combination with low surfaceenergy has been required to obtain the so called superhydrophobicsurfaces. Superhydrophobicity is variously reported as a materialexhibiting a contact angle with water that is greater than contactangles achievable with smooth but strongly hydrophobic materials. Theconsensus for the minimum contact angle for a superhydrophobic substanceis 150 degrees, so in this context some of the embodiments of thepresent invention are not strictly superhydrophobic, although thisoption is not excluded The reason for this is that a Wenzel-Cassie statelies in its hydrophobicity between nontextured surfaces and surface thatgenerate a Cassie-Baxter interface. In optimizing the adherence of thetextiles of the present invention superhydrophobicity is just one aspectof a number of interesting texture controlled mechanisms, and in thiscontext the contact angle is less important than the contact anglehysteresis.

It is known in the art that the transition to the Wenzel state can bediscouraged by the use of sharp cornered features in the plane of thesurface. However, the occurrence of sharp cornered structures in naturalstructures, such as rose petals, is less common. Natural structures tendto possess rounded surface features, especially radiused or filletedcorners. In nature, resistance to conversion to a Wenzel state seems toinvolve the creation of involute rounded structures rather than sharpedges. By involute it is meant concavity oriented in a line notorthogonal to the substrate surface. Such structures are difficult tocreate by an etching or casting method, but can readily be created by anembossing method that entails folding of a structure.

Similarly, the Wenzel state can be discouraged by the use of curvingcommunications between structures as opposed to straight linecommunication. In most cases, higher hydrophobicity equates with lowerpropensity for a Wenzel transition. The hydrophobicity of a surface isenhanced by the placement of exterior corners around depressions. Insome embodiments, this is achieved by the creation of additional pairsof adjacent depression walls that project into and are joined at theinterior of the depression. In some embodiments this is achieved bydesigning an ordered array of depressions of a first hierarchy(examples: triangular, rectangular, pentagonal, or hexagonal shapes,regular or irregular; and further polygonal shapes defined generally bystraight line segments).

A second feature of smaller size and different hierarchical order isthen superimposed on the depression wall of the first pattern. Themethod employed in creating such a structure may involve first emboss alarge scale structure and then secondarily emboss additional smallerscale structure, preferably smaller scale structure embossed on largerscale structures.

Water possesses a dipole structure which makes it attractive to anyother substance that is charged. Molecules with a charge surpluslocalized at a specific location on the molecule renders that moleculehydrophilic. In the case of polymers, the charges can associate, and thebulk substance and possess a macroscopic charge. And in such macroscopicassemblages, such materials are strongly water attractive. And whenthose macroscopic charge localities are associated with surface texture,than a substance becomes superhydrophilic. The term superhydrophilic hasvarious meanings in the literature, and in many cases simply refers tothe rendering of a substance more hydrophilic, or a decrease in contactangle relative to a flat surface of the same substance. Here, it ismeant the accentuation of surface charge and surface energy such thatwater is always bonded to the substrate surface, even though anyparticular water molecule may have a short residence time on the polymersurface. This has a commercial advantage in that the adherent surface ofthe low normal force retractor is both shielded from contaminatingdebris and also is self-washing due to the stochasticattachment/detachment of water molecules from the surface. The methodsof manufacture of textured surfaces low normal force retractors of thepresent invention include lithography, casting, extrusion/embossing, andany of several methods for transferring a texture to a surface. Methodsfor forming such hierarchical microstructured surfaces are described inU.S. application Ser. No. 14/802,632, which is hereby incorporated byreference in its entirety.

A preferred method is embossing, where a polymeric substance is heatedto a molten state and passed through dual rollers, at least one of whichcontains a negative image of the desired embossed structure. A smallscale texture is embossed on a planar sheet. This embossed planar sheetis heated to a malleable but not fluid state and passed through dualrollers possessing a medium scale texture which impresses an inverseimage. This process can be repeated multiple times. The medium scaletexture is large relative to the small scale texture, thus theimpression of the medium scale texture folds the small scale texture,making possible involute structures which would ordinarily not bepossible with a lithography or casting method.

The low normal force retractors of the present invention have three ormore levels of textures assembled in a manner to yield a high surfacearea while maintaining a minimum spacing between textures to allow forliquid flow and penetration to promote in the first instance surfacewashing and in the second instance surface adhesion; and whilemaintaining a minimum structural strength obtained by keeping height towidth aspect ratio of all features below a critical level at whichmaterial strength is exceeded.

Referring to FIG. 5, a first embodiment of a low normal force retractorarrangement 500 on a textile surface according to the present inventionis shown comprising a substrate, designated generally as 510. In theillustrated embodiment, substrate 510 has a sinusoidal waveformcomprising a series of rounded peaks and valleys that produce acontinuously curving surface across at least a portion of substrate 510.The sinusoidal waveform of substrate 510 defines a first set of largescale features, designated generally as 512, while a second set ofmicrofeatures, 514 are disposed on the large scale features.

In FIG. 5, substrate 510 is constructed and arranged to focus on aseries of rounded knobs forming peaks 515 projected upwardly from thesurface with associated valleys 517 disposed between peaks 515.

In a second embodiment shown in FIG. 6, the inverse arrangement is shownin which substrate 610 is constructed and arranged to focus on a seriesof rounded cavities forming valleys 617 extending inwardly intosubstrate 610 as the dominant feature with the associated peaks 615disposed between valleys 617, and 614 indicates a second set ofmicrofeatures. In both embodiments, the surface of substrate 610 iscontinuously curving throughout sinusoidal waveform pattern area.

According the present invention, the term sinusoidal waveform as usedherein refers to a surface having a repetitive oscillation of rounded,nonflat curvature described by mathematical formulas incorporatingtrigonometric functions sine, cosine, tangent or exponential and powerseries functions. These mathematical formulas are used in computer aideddesign and computer aided manufacturing software to create texturesurfaces using rapid prototyping, milling, electrical dischargemachining or similar techniques to create a polymer or metal surfacewith the sinusoidal waveform texture features. The advantage of usingmathematical formulas is that large numbers of rounded, nonflat featurescan be created rapidly in computer aided design and computer aidedmanufacturing software. Texture features of this type cannot be createdusing lithographic techniques.

Referring to FIGS. 7A-7D, a selection of substrates 710 are shown havingvarious sinusoidal waveform patterns that provide alternative curvedsurface texture features across substrate 710. These embodiments are forillustrative purposes only as example embodiments of substrate 710 andare not limiting of the present invention and the term sinusoidalwaveform as used herein. According to the present invention, first setof texture features 712 includes dimensions selected from a size withina range of about 100 microns to about 1000 microns. More specifically aswill be detailed herein below, in a preferred embodiment, the sinusoidalwaveform is arranged so that first set of texture features 712 hassinusoidal rounded cavities of 750 microns, a pitch of 750 microns, anda depth of about 240 to 500 microns. This arrangement of the substrateis intended to promote an adhesive Wenzel-Cassie state with ahydrophobic/hydrophilic contact mixture. Referring to FIGS. 8 and 9, asecond set of texture features 814 and 914 are disposed on the surfaceof substrate 810 and 910. In one embodiment, second set of texturefeatures 814 is molded on first set of texture features 812 and 912 ofsubstrate 810 and 910, respectively. As detailed herein below, in apreferred embodiment, substrate 810 or 910 is a compression moldedpolymeric material in which first and second sets of texture features812, 814 and 912, 914 are formed on substrates 810 and 910,respectively, during a single molding step. First and second sets oftexture features 812, 814 cooperate to increase the surface area andaffect at least one of adhesion, friction, hydrophilicity andhydrophobicity of substrate 810 and 910. Preferably, the compressionmolded polymeric material forming substrate 810 is an environmentallydurable polymer. In one embodiment, substrate 810 or 910 comprisespolyethylenenylon copolymer. In the illustrated embodiments, second setof microstructures 814 or 914 is selected from the group consisting ofmicrostructured projections and microstructured cavities, andcombinations thereof. In the illustrated embodiment in FIG. 6, secondset of texture features 614 comprise microstructured cavities extendingdownwardly into substrate 610.

In the illustrated embodiments of FIGS. 8-11, second set of texturefeatures 814, 914, 1014 and 1114 comprise microstructured projectionsextending upwardly from substrate 810, 910, 1010, and 110, respectively.Preferably, in the illustrated embodiments of FIGS. 8-11, themicrostructured projections of said second set of texture features 814,914, 1014 and 1114 comprise generally cylindrical pillars.

Preferably, in the illustrated embodiment of FIG. 6, the microstructuredcavities of second set of texture features 614 comprise generallycylindrical recesses.

Referring to FIG. 9, in one embodiment in which substrate 910 is a thinfilm substrate and has operable opposing top and bottom surfaces, firstset of texture features 912 disposed on a top surface 921 of substrate910 form a complementary shape on a bottom surface 923 of substrate 910so that a rounded peak on top surface 921 forms a rounded valley onbottom surface 923 and the rounded valley on top surface 921 forms arounded peak on bottom surface 923.

Again referring to FIG. 9, in an embodiment in which substrate 910 is athin film substrate and has operable opposing top and bottom surfaces,second set of texture features 914 includes a series of microstructuredprojections on one of top surface 921 and bottom surface 923 ofsubstrate 910, which then define a series of complementarymicrostructured cavities on the other of said top surface and saidbottom surface 921, 923.

Likewise, in an embodiment in which second set of texture features 914comprises microstructured cavities which project downwardly throughsubstrate 910 from a top surface 921, they form complementarymicrostructured projections on the opposing bottom.

Referring to FIGS. 5, 8 and 9, in the illustrated embodiments, secondset of texture features 514, 814 and 914 include at least a portion oftexture features that extend along an axis normal to the curve of thesinusoidal waveform of substrate 510, 810 and 910 at a given point forthe individual microstructure. In this way, the second set of texturefeatures follow the curvature of first set of texture features 512, 812and 912.

According to the present invention, second set of texture featuresincludes dimensions selected from a size within a range of about 10microns to about 100 microns. Further, second set of texture featurespreferably have a height to width aspect ratio of less than 5, and aminimum spacing of 1 micron between each texture feature of said secondset of texture features to maintain structural strength while allowingfor liquid flow and penetration between the individual microstructurescomprising second set of texture features.

Referring again to FIGS. 8-11, a third set of texture features 820, 920,1020 and 1120 may also be disposed on substrate 810, 910, 1010 and 1110,respectively. Preferably, third set of texture features 820 is selectedfrom the group consisting of microstructured projections andmicrostructured cavities, and combinations hereof. In one embodiment,the microstructured projections of third set of texture features 820,920, 1020 and 1120 comprise generally cylindrical pillars.

Referring to FIG. 6, in one embodiment, the microstructured cavities ofthird set of texture features 620 comprise generally cylindricalrecesses. Preferably, third set of texture features 620 are compressionmolded simultaneously with first and second sets of texture features612, 614. In a further preferred embodiment, third set of texturefeatures 620 have a height to width aspect ratio of less than 5, and aminimum spacing of 1 micron between each texture feature of third set oftexture features 620 to maintain structural strength while allowing forliquid flow and penetration between said third set of texture features.The aspect ratio is smaller when devices are made of lower strengthmaterials and larger when made from stronger materials. The spacingbetween features is smaller for less viscous liquids and larger for moreviscous

Referring to FIGS. 5, 8, 9, third set of texture features 520, 820 and920 include at least a portion of texture features that extend along anaxis normal to the curve of the sinusoidal waveform of substrate 10. Forpurposes of the present invention in which the second and third sets oftexture features extend along an axis normal to the curve of thesinusoidal waveform, the normal line to a curve is the line that isperpendicular to the tangent of the curve at a particular point. In theillustrated embodiments, second set of texture features 514, 814 and 914is smaller than first set of texture features 512, 812 and 912,respectively, and third set of texture features 520, 820 and 920 issmaller than second set of texture features 514, 814 and 914,respectively According to the present invention, the third set oftexture features includes dimensions selected from a size within a rangeof about 1 micron to about 10.

Referring to FIGS. 5 and 8-11, in one embodiment, third set of texturefeatures 520, 820 and 920 are disposed on an end surface 522, 822 and922 of second set of texture features 514, 814 and 914. In a furtheradvantageous embodiment, third set of texture features 520, 820 and 920are disposed on first set of texture features 12 between second set oftexture features 14. In a further advantageous embodiment, third set oftexture features 20 are disposed on an end surface 22 of second set oftexture features 14, as well as, disposed on first set of texturefeatures 12 between second set of texture features 14. 30

Referring to FIGS. 10 and 11, a fourth set of texture features 1024 and1124 may be disposed on side surfaces of second set of texture features1014 and 1114, respectively. Fourth set of texture features 1024 and1124 is selected from the group consisting of flutes 1016, 1116 and ribs1018, 1118 and combinations thereof. In the illustrated embodiments,flutes (1016, 1116) and ribs (1018, 1118) run vertically along theheight of the side surfaces on the outside circumference of eachmicrostructure comprising said second set of texture features (1014,1114). The fourth set of texture features preferably include dimensionsselected from a size within a range of about 1 micron to about 10microns. Preferably, fourth set of texture features 1024 and 1124 arecompression molded simultaneously with said first, second, and thirdsets of texture features into substrate 1010, 1110.

Preferably, flutes and/or ribs (1016, 1018, 1116, 1118) with featuresand spacing larger than 1 micron are added to the exterior of thecylindrical pillars or cavities defining second set of texture features(1014, 1114) to both add surface area and to increase structuralresistance to bending and breaking. The spacing between individualmicrostructures of fourth set of texture features 1024, 1124 and betweenindividual microstructures of second set of texture features (1014,1114) is smaller for less viscous liquids and larger for more viscousliquids.

Third set of texture features (1020, 1120) cover both the tops ofpillars and bottoms of cavities and the area between the pillars orcavities defining second set of texture features 1314 in a substantiallyuniform manner. Together the second and third sets of texture features(1014, 1114), (1020, 1120) substantially increase the surface areaexposed to the liquid covering the opposite surface from the substrate.Depending on the desired application, the first, second, third andfourth sets of texture features cooperate to increase the surface areaof substrate (1010, 1110) to effect at least one of adhesion, friction,hydrophilicity and hydrophobicity of the substrate. In one embodiment,substrate (1010, 1110) has a surface adhesion with a sliding frictionforce of greater than 50 gr/cm2 when applied against a surface comprisedof a hydrophobic/hydrophilic mixture. In a preferred embodiment, thesubstrate (1010, 1110) has a surface adhesion with a sliding frictionforce of about 325 gr/cm2 when applied against a surface comprised of ahydrophobic/hydrophilic mixture.

In early studies, the inventors characterized rose petal structures andobserved a ‘rolling hill’ effect in microstructures. Additionally,smaller microstructures were noted as ‘hairs’ that seemed to contributestrongly to the superhydrophobic effect. In order to best simulate thisscheme, the inventors created sinusoidal designs as set forth hereinthat could reproduce and improve upon rounded microstructure effectsseen naturally, starting with a sinusoidal waveform substrate withfeatures from 300 microns diameter and pitch of 100 microns.

The dimensions for the third set of texture features (1020, 1120)include in one embodiment pillars having 3 micrometers diameter, 6micrometers pitch, and 5 micrometers tall. The second set of texturefeatures (1014, 1114) in one embodiment includes fluted microstructurepillars that are at least 35 micrometers in diameter, 35 micrometerstall, and 10 micrometers spacing. When overlapped together, the secondand third sets of micro features (1014, 1114, 1020, 1120) are formedalong an axis normal to the surface of the sinusoidal waveform features.These are also maintained multidimensionally over the round.

To improve the superhydrophobic effect found in nature with the rosepetal, second set of texture features (1014, 1114) was added with‘fluted’ or ‘ribbed’ features running down the side surface. Thesefluted and ribbed features that define fourth set of texture features(1024, 1124) simulate the smaller, hair like microstructures of the rosepetal to further promote hydrophobicity. Accordingly, eachmicrostructure of said first, second, third and fourth sets of texturefeatures have a respective pitch, height/depth, and diameter, andwherein are arranged so that liquids penetrate between at least saidfirst and second sets of texture features in a Wenzel fully wetted statewhen applied against a liquid covered surface to promote adhesionbetween the substrate and the adjacent surface. Preferably, thesinusoidal waveform of the first set of texture features includesrounded peaks that facilitate pressure distribution across the substratewhen pressed against a liquid covered surface.

Preferably, the second and third sets (1014, 1020, 1114, 1120) oftexture features are uniformly distributed across the rounded peaks offirst set of texture features to provide increased surface area to firstset of texture features. The rounded peaks define areas of increasedpressure when the substrate is applied against a liquid covered surfacethat promote a transition of liquid droplets from a suspendedCassie-Baxter state to a Wenzel fully wetted state among at least saidfirst and second sets of texture features. In a preferred embodiment,first, second and third sets (1012, 1112, 1112, 1114, of texturefeatures allow for liquid penetration to a Wenzel fully wetted state,while the fourth set of texture features (1024, 1124) are constructedand arranged to maintain superhydrophobic characteristics.

The function of the second and third sets of texture features is tocreate a large surface area simultaneously with spacing wide enough theviscous liquids can flow through the structure at low pressure. Lowpressure in this application is defined in the context of the weightassociated with liquid droplets being sufficiently to create a Wenzelfully wetted state to promote adhesion of substrate 10 to an adjacentliquid covered surface. Accordingly, the microstructured surfaces of thepresent invention are designed to facilitate transitions from aCassie-Baxter suspended droplet state to the Wenzel fully wetted statewith a water droplet of greater than 10 texture liters in size.

One function of the sinusoidal waveform of first set of texture featuresis to further increase the surface area while creating areas ofincreased pressure at the peaks of the features. These areas ofincreased surface area wet first, causing a rapid transition from theCassie-Baxter suspended droplet state to the Wenzel fully wetted state.A second function of the sinusoidal waveform of first set of texturefeatures is to keep the peak pressure low enough and to spread thepressure such that there is little or no penetration through the liquidlayer on the surface into the underlying material. The second and thirdsets of texture features are spread uniformly over the sinusoidalwaveform of first set of texture features and are normal to the curve ofthe surface. That is they are perpendicular to a surface tangent at eachpoint of the microstructure on surface. This ensures that the maximumsurface area is created in a structure that can be molded.

Specific Embodiments Rotus Type I

FIG. 12 is a perspective view of a hybrid rotus Type I retraction deviceaccording to a third embodiment of the invention. Device 1200 iscomprised of rose texture side 1210 and lotus texture side 1212. A rosetexture 1210 is characterized by the geometry of a water drop 1214wherein drop 1214 takes on a spherical shape 1216 characteristic of asuperhydrophobic surface. Drop 1214 is immobilized on the surface 1210due to wicking geometry 1218. A lotus texture 1212 is characterized bythe geometry of water drop 1220 wherein the shape is spherical with theabsence of a wicking structure analogous to feature 1518. Drop 1220resists adhesion to surface 1212, and readily rolls off the surface.

Corrugated Type II

FIG. 13 is a side view of a corrugated Type II retraction deviceaccording to a fourth embodiment of the invention. It should beunderstood a manually actuated Type I version is also possible. Device1300 can be in two configurations 1310 and 1312. Configuration 1310 is arose texture configuration and configuration 1312 is a lotus textureconfiguration. Thus, when in configuration 1610 device 1300 is adhesive,and in configuration 1312 it slides easily. Device 1300 in thecorrugated state 1310 has first structure 1314 and second structure1316. An inflation member 1320 causes device 1600 to move in direction1318 to transform into configuration 1312 when pressurized.

Area Changing Type II

FIG. 14 is a perspective view of a area changing Type II retractiondevice according to a fifth embodiment of the invention. Device 1400 hassurface texture 1314 and can be in two configurations 1310 and 1312.Configuration 1310 is a flat configuration with maximum surface area incontact with a planar surface and configuration 1612 is an inflatedconfiguration with minimum surface area. Thus, when in configuration1310 device 1300 is adhesive, and in configuration 1312 it slides moreeasily. An inflation member 1316 causes device 1300 to transform intoconfiguration 1312 when pressurized.

Area Changing Type I

FIG. 15 is a side view of a hybrid area changing Type I retractiondevice 1500 where the textured area 1514 is unchanging according to asixth embodiment of the invention. Device 1500 assumes two bistableconfigurations 1510 and 1512. In configuration 1510 rose petal texture1514 is the only surface presented to another surface to which device1500 is to adhere. The contact surface area in configuration 1510 is thesum of the areas of 1514. The area 1516 is smooth, and the area ofconfiguration 1512 is larger than the area of configuration 1510. Thearea of configuration 1512 is the sum of the areas 1514 and 1516.Configuration 1512 is achieved by pulling configuration 1510 in thedirections 1518.

Pincer Type II

FIG. 16 is a perspective view of a pincer movement Type II retractiondevice 1600 according to a seventh embodiment of the invention. Device1600 has a relaxed, conformable state 1610 and rigid pinching state1612. Transformation from state 1610 to state 1612 is achieved byinflation element 1616. Features 1614 comprise a rose petal adhesivesurface.

FIG. 17 depicts a retractor 1701 comprised of arm 1703 and surgicalanchor 1705. The surgical anchor 1705 enables the surgeon to anchor theretractor 1701 to perioperative surgical dressing. The proximal end 1707of the retractor 1701 possesses superhydrophobic surface 1019. Detailedexamples of superhydrophobic surface are depicted and described above.Optionally, the retractor may comprise an inflation element 1711comprised on a hallow section 1713 that can be pressurized via tube1715. As depicted, when hallow section 1713 is inflated the retractorbecomes rigid and straight along direction 1717. Optionally, theretractor may comprise a suction bladder comprised of a series of holes1719 providing throughput from tissue contacting side 1721 to internalsuction volume 1723. The suction bladder is comprised of the tissuecontacting side 1721 and an external side 1725. External side 1725 maypossess tabs 1726 to which a surgeon may suture a stay line or grasp toposition retractor 1 relative to a tissue surface. A suction tube 1727attached to the suction bladder provides suction and draws tissue fluid1729 into the suction bladder. Optionally retractor 1 may possess apreformed shape such that the width 1731 is straight and the length 1733is curved with radius of curvature 1735. Optionally, the retractor 1701possesses a tissue contacting surface 1721 which is corrugated 37. Thecorrugation frequency 1739 can be adjusted through inflation element1711, such that increased inflation decreases frequency 1739 andincreases length 1733.

All references cited herein are hereby incorporated by reference intheir entirety.

We claim:
 1. A microstructured retractor comprising at least one armhaving a superhydrophobic surface comprised of at least one of aWenzel-Cassie surface, Cassie-Baxter surface, or combination of thesesurfaces, wherein when placed on a wet surface the shear force requiredto move the microstructured retractor along the wet surface exceeds theapplied normal force.
 2. The microstructured retractor of claim 1,further comprising an inflation element, wherein the inflation elementprovides adjustable rigidity to the microstructure retractor.
 3. Themicrostructured retractor of claim 1, wherein a suction element isattached to provide fluid removal while the microstructure retractor isin use.
 4. The microstructured retractor of claim 1, wherein theretractor possesses a shorter dimension called the width and a longerdimension called the length, and said retractor is comprised of aflexible material capable of being preformed with an innate curvature,wherein the width has essentially zero curvature and whereas the radiusof curvature in the length dimension is less than the length.
 5. Themicrostructured retractor of claim 1, wherein the retractor iscorrugated in a direction such that when the retractor is placed on awet surface only a portion of the microstructured surface is in contactwith the wet surface, and wherein the corrugation is adjustable bypermanent deformation of the microstructured retractor so as to changethe amount of the surface of the microstructured retractor in contactwith the wet surface.
 6. The microstructured retractor of claim 5,wherein the corrugation is reversibly deformable and the retractorfurther comprises an inflation element such that when inflated thecorrugation frequency reversibly changes, and further the inflationelement comprises a valve such that the inflation volume can becontrolled.
 7. The microstructured retractor of claim 6, wherein anadditional inflation element is incorporated that reversibly stiffensthe microstructured retractor when inflated.
 8. The microstructuredretractor of claim 5, wherein a first corrugation state is in aWenzel-Cassie state when in contact with a wet surface and a secondcorrugation state is in Cassie-Baxter state when in contact with a wetsurface.
 9. The microstructured retractor of claim 1, wherein one sidecomprises a Wenzel-Cassie microtextured surface and the other sidecomprises a Cassie-Baxter microtextured state.
 10. A microstructuredretractor of claim 1, wherein a first arm has at least one surfacecomprising a Wenzel-Cassie surface and a second arm has at least onesurface comprising a Cassie-Baxter surface.
 11. The microstructuredretractor of claim 1, wherein the at least one arm comprises at leastone rose-mimic surface.
 12. The microstructured retractor of claim 1,wherein the at least one arm comprises at least one lotus mimic surface.13. The microstructure retractor of claim 1, wherein at least a portionof the arm comprises a superhydrophobic surface.
 14. The microstructureretractor of claim 5, wherein at least a portion of the arm comprises asuperhydrophobic surface.
 15. The microstructure retractor of claim 1,wherein at least a portion of the retractor comprises a surface havingcontact angle hysteresis greater than 5 degrees when in contact with awet surface.
 16. The microstructure retractor of claim 5, wherein atleast a portion of the retractor comprises a surface having contactangle hysteresis greater than 5 degrees when in contact with a wetsurface.